1. Field of the Invention
The present disclosure relates to a method for treating a hexavalent chromium-containing aqueous solution.
2. Description of Related Art
In resent years, the use of a photocatalyst has been expected as means for treating water containing a predetermined pollutant. For example, Yuko Maruo and two other persons state that a medical drug contained in water can be decomposed and removed by a titanium dioxide photocatalyst (“Development of dispersion-type TiO2 photocatalyst for decomposition of medical drugs in water”, Book of Preprints of The 77th annual meeting of The Society of Chemical Engineers, Japan, Public Interest Incorporated Association The Society of Chemical Engineers, Japan, March 2012, p. 427). In addition, Limin Wang and two other persons state that hexavalent chromium can be reduced into trivalent chromium by photocatalytic reaction of titanium dioxide, and that the presence of coexisting organic substances and the surface area of the titanium dioxide influence the reduction rate (“Photocatalytic reduction of Cr(VI) over different TiO2 photocatalysts and the effects of dissolved organic species”, Journal of Hazardous Materials, Mar. 21, 2008, vol. 152, No. 1, p. 93-99). In addition, in order to facilitate solid-liquid separation of photocatalyst particles dispersed in water, it has been proposed to use a photocatalyst in which titanium dioxide particles are immobilized by a binder such as a binding agent on support particles having a larger particle diameter than the titanium dioxide particles (see JP 10-249210 A, for example). In addition, a technique has been proposed that uses a photocatalyst obtained by coating support particles with titanium dioxide by a coating process such as a sol-gel process (see JP 11-500660 T, for example).